Storage type acoustic image converter device and acoustic viewing system

ABSTRACT

An electron discharge device is provided for a system involving illumination by suitable sonic energy radiator means of any opaque, turbulent or dense medium and converting the returned acoustic signals into a video output signal for remote or direct display. Storage, as well as integration of acoustic signals through a process of correlation in a device having a unique crossed field electron beam deflection system is provided together with the signal impinging and generation means in an integral evacuated envelope. A non-scanning flood type electron beam continuously samples the voltage on an acoustic-responsive conversion plate and yields a modulated secondary electron emission beam whose phase and amplitude is that of the impinging acoustic signals.

United States Patent Osepchuk [451 Apr. 4, 1972 3,474,286 10/1969 Hergenrother ..3 15/12 Primary Examiner-Richard A. Farley Att0rney--Harold A. Murphy, Joseph D. Pannone and Edgar [72] Inventor: John M. Osepchuk, Concord, Mass. 0. Rest [73] Assignee: Raytheon Company, Lexington, Mass. [57] ABSTRACT 2 F'l b. [2 1 1 ed Fe 1970 An electron discharge device 15 provided for a system involv- [21] Appl. No.: 14,375 ing illumination by suitable sonic energy radiator means of any opaque, turbulent or dense medium and converting the returned acoustic signals into a video output signal for remote [52] or direct display. Storage, as well as integration of acoustic [51] Int Cl G015 9/66 signals through a process of correlation in a device having a [58] Fieid MP unique crossed field electron beam deflection system is pro- 5 75/63 vided together with the signal impinging and generation means in an integral evacuated envelope. A non-scanning flood type [56] References Cited electron beam continuously samples the voltage on an acoustic-responsive conversion plate and yields a modulated UNITED STATES PATENTS secondary electron emission beam whose phase and amplitude 2 652 51s 9/1953 M G 313/79 x is that of the impinging acoustic signals.

c ee 2,848,890 8/1958 Sheldon ..340/5 MP 14 Claims, 6 Drawing Figures t E TH MODULATED IMAGE ORTHICON SECTION 7 SECONDARY 66 ELECTRON B IMAGE PIEZOELECTRIC PLATE 1 86 ACOUSTlC l IMAGE I 76 t, 1 o 6 t use 1 a J L l 64 BEAM 3 UNIFORM ELECTRON IMAGE TARGET CROSSED-FIELD DEFLECTION PLATES AT POTENTIALS I DIRECTED AT PIEZOELECTRIC l l l It:ree l l -v PHOTOCATHODE ENVELOPE PATENTEDAPII 4 I972 SHEET 1 [IF 2 5 31-1: DENSE I MEDIUM 2 I: o 4 PROJECTOR I3 POWER C SouRCE S PROCESSING CIRCUITS IMAGE Fig DISPLAY TRANSMISSION UM 0 SECONDARY o SCANNING :3. -E-1:-- ELECTRONS o BEAM o FOCUSED CHARGE ACOUSTIC IMAGE Z ENERGY 26 o SCREEN w CONVERSION 24 LIJ E 8 PLATE VACUUM 5g 0 PRIOR ART 0 z o 8 a; F g U) O.

o I 4 (T56 F 9 4 m 52 I z 3 I g 54 I L62 2 I A I E I I i [NI/EH70}? g 58 I JOHN M. OSEPCHUK z 7 B E 8 ENERGY OF PRIMARY ELECTRONS INCIDENT Y 5% ON TARGET ATTORNEY STORAGE TYPE ACOUSTIC IMAGE CONVERTER DEVICE AND ACOUSTIC VIEWING SYSTEM BACKGROUND OF THE INVENTION visible image.

2. Description of the Prior Art In the field of interest the development of natural resources and navigation of the ocean environment has created a demand for new and useful devices as well as viewing systems, particularly in highly turbid or murky waters. Additionally, physicians as well as medical researchers require means for examining internal body tissues without the damaging effects of X-rays and especially in soft tissue structures where radiography is ineffective. Another group interested in devices within the field of the invention are engineers and manufacturers concerned with non-destructive testing of fabricated articles involving testing of welds, castings and other structures for hidden flaws. The opaque nature of the medium under investigation, therefore, is of primary concern.

A device and system proposed in the past involves acoustic imaging somewhat similar to television utilizing acoustic waves rather than light waves in forming an object image. Devices including sensors as well as converters for acoustic viewing systems have received the attention of numerous researchers and scientists since perhaps the earliest work of S. Sokolov of Russia approximately 30 years ago. In US. Pat. No. 2,164,125, issued in 1939, a mechanical system is disclosed by this inventor. In 1949 an electronic device was described by him in an article entitled An Ultrasonic Microscope" CR. Acad. Sci. USSR 64, P333, 1949 and J. Techn. Phys. USSR 19, P.27, 1949, both translated from Russian in Radio Electronic Engineering, 8-9, Feb., 1953. This latter device provided for a quartz plate as a part of an oscilloscope tube onto which an acoustic image is focused. From the back of the tube secondary electrons are produced, picked up by a scanning electron beam and transferred into an optical output. This device is exemplary of the so-called scanning electron beam technique. Numerous investigators of this technique have submitted a number of proposed structures in an attempt to improve such devices. The practical art limitation, however, appears to be one of sensitivity and it has been stated by Jacobs that the theoretical limitation of such devices is about 10" W/cm on the face of the image converter. Reference may be had to the article An Investigation of the Limitations to the Maximum Attainable Sensitivity in Acoustical Image Converters, J. E. Jacobs, H. Berger, and W. J. Collis, IEEE Trans. Ultrasonic Engineering, UE-lO, pps. 83-88, September 1963 for further information on this subject.

In view of the sensitivity limitation proposals have arisen in the art involving the utilization of many radical departures from the scanned beam techniques. These techniques, in one way or another, all involve storage of intelligence and have promise of greater sensitivity and perhaps better resolution. One system provides for the coupling to the piezoelectric input surface of a series of rnicrominiature germanium or silicon diodes with the function of the diodes being to rectify the alternating piezoelectric voltage and permit storage of this voltage .on small distributed condensers. In US. Pat. No. 2,957,340, issued to H.A.F. Rocha on Oct. 25, 1960, a fuller description of this technique is provided. To date, however, performance characteristics of such tubes have remained unreported. An additional approach involves the use of materials of a particular piezoresistive characteristic to provide a resistivity in the order of 12 ohm cm to permit storage. Cadmium sulphide crystals have been utilized, however, apparently the device has not proceeded beyond the experimental stage.

Another attempt at the provision of a storage type image converter involves the use of a non-scanned type electron beam. US. Pat. No. 2,848,890 issued Aug. 26, 1958 to E. E.

Sheldon discloses a technique involving a flooding electron beam modulated by the piezoelectric voltage on the input surface. The modulated secondary electron emission image is caused to impinge on a fluorescent screen for direct viewing. This tube, however, is not suitable for remote viewing and has not received wide usage in the art. A general discussion of the aforementioned art, as well as numerous other proposals in the field of acoustic image sensing devices, may be had by reference to the report Ultrasonic Imaging" Proc. Symposium Mine Advisory Committee, April, 1965, National Academy of Sciences, National Research Council NRC:MAC:2016, Report AD621372.

In summary, all of the foregoing devices have a common disadvantage as far as sensitivity or resolution characteristics to limit their usefulness in acoustic image conversion and viewing systems. Efforts to improve these parameters have met with little success and are in fact, limited by theoretical considerations in electron beam devices. It appears to some reviewers that the problem in the provision of an improved electronic underwater viewing system resides in storage of image sensing signals. With new and even greater frontiers being developed in the so-called inner space" to explore our resources together with the heretofore described medical and manufacturing fields of interest, the provision of improved electronic acoustic image sensing and converting means becomes of paramount importance.

SUMMARY OF THE INVENTION The novel concept of the present invention commences with the realization that scan-type acoustic image converting devices of the prior art, while offering the greatest potential for real time image conversion are limited in sensitivity insofar as tube electronics are concerned, primarily, by the shot noise in the beam and low beam conductance. The piezoelectric target electrode in such devices simply provides for a voltage buildup at a particular point or resolution cell. The impingement of the focused acoustic image on the target electrode results in alternate displacement of the surface potential on the plate which is essentially a dielectric capacitor to result in the introduction of an AC modulation component in the scanning beam current. As a result, the signal in the beam current is this AC component which is generally much smaller than the DC beam level. In order to improve sensitivity, therefore, in such devices by storage techniques as suggested by Turner in one of the articles published in the aforereferenced report Ultrasonic Imaging, as well as other researchers in this field, the AC modulation factor must be considered. Further, in achieving a storage parameter for acoustic image conversion devices and systems the AC converted acoustic signals require the introduction of some rectification or correlation for integration and storage in order that the average electron emission to be fed to an output signal producing means may be related and controlled by the acoustic image signals.

The processing of the acoustic image signals including integration and storage are provided in accordance with the teachings of the present invention utilizing secondary electron emission characteristics. In addition, correlation of electrical signals will result in highly resolved output signals for video presentation thereby increasing the sensitivity of the viewed acoustic images by a factor of approximately 10 together with measurable improvement in contrast.

The novel storage type acoustic image device provides for a non-scanning uniform primary electron flood beam generated by a suitable source, such as photocathode or electron gun, which traverses a crossed field deflection region to bombard the internal side of an offset acoustic image target conversion plate. The target plate is at a potential adjusted to the predetermined crossover point of the piezoelectric material to thereby optimize emission of secondary electrons. The piezoelectrically induced voltage on conversion plate creates a beam modulation of the secondary electron emission beam at the acoustic frequency w, as a return beam. The composite return beam after suitable deflection by the crossed field means impinges on an offset correlator section comprising a storage target member, target mesh screens, and electron multiplier section. These components are substantially similar to ones utilized in electrooptical correlator devices of the image orthicon type. Regions of larger acoustic signal intensity will produce a larger secondary electron emission signal modulation. Conversely, regions of lower acoustic signal intensity will produce lower modulation on the secondary electron beam. In the image correlator section an electrical reference drive signal introduced by suitable means such as a biased target mesh screen will provide for the integration of the secondary electron emission modulation. The correlation process with appropriate storage and multiplier means yields an integrated video frequency electrical output signal representative of the original piezoelectrically induced voltage potential fluctuations proportional to the sensed acoustic image signals.

The disclosed device is immersed in a uniform magnetic field and incorporates in an integral arrangement multiple signal processing sections intercoupled by the crossed field deflection arrangement for both the primary and secondary electron image beams. The stored detected acoustic image signals are integrated through a correlation process similar to the processing of optical image signals in image orthicon devices with corresponding cancellation of acoustic noise and improvement in sensitivity. In addition, the phase relationships provided by the disclosed device will assist in topological investigation of subsurface or underseas areas to now provide an excellent tool in this area. A practical underwater viewing system utilizing the disclosed acoustic image converter device will be provided for use in all opaque environmental conditions, as well as non-destructive examination for material structural defects utilizing acoustic imaging techniques.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the details for the provision of a preferred embodiment, will be readily understood after consideration of the following detailed description in reference to the accompanying drawings, wherein:

FIG. 1 is a schematic representation of an illustrative acoustic imaging system;

FIG. 2 is a pictorial representation of prior art acoustic image conversion techniques;

FIG. 3 is a block diagram illustrative of the embodiment of the present invention;

FIG. 4 is a plot diagram illustrative of the secondary electron emission characteristics utilized in the embodiment of the invention;

FIG. 5 is a schematic representation of the embodiment of the invention;

and FIG. 6 is a cross-sectional view of a crossed field deflection arrangement for utilization in an illustrative embodiment of the invention oriented along the line 6-6 in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 illustrates diagrammatically the essential components of an acoustic viewing system. A directional acoustic energy projector 2 powered by a suitable power source 4 insonifies the object 6 under evaluation or surveillance. The sound waves reflected and scattered back from the object are collected by an acoustic lens 8 disposed at one end of the overall image sensing and converting means. Coupling medium 10 is desired to provide impedance matching between the environmental medium and the sensing means. A suitable exemplary medium would be a vacuumdistilled silicone oil under relatively low pressure. The collected energy rays are thereby focused on the piezoelectric or electrostrictive transducer plate 12 to form a two-dimensional acoustic image projection. The plate 12 transforms the acoustic image signals into corresponding electron charges which are sensed and converted by an electron discharge device such as an image orthicon tube 14 of the type used in processing television signals. The processing electronic circuits 16 for scanning and readout result in the generation of a video output signal to activate display means 18.

In FIG. 2 a more comprehensive illustration to explain the image conversion phenomenon in an acoustic viewing system will be noted. The basic components include the transducer conversion plate 12 which serves as an interface on one side for the transmission medium 10 through which the focused acoustic energy rays are propagated. On the reverse side of the plate an electron beam 22 scans the converted electric signal pattern to modulate secondary electrons emitted from surface 20 which may be sensitized to provide an effective emission ratio of unity or higher. To facilitate optimum modulation of the return electron beam a mesh screen member 24 with a suitable DC bias may be provided adjacent to the surface 20 of the conversion plate 12.

The electrical signals on the conversion plate resulting from the impinging focused acoustic energy yields a charge image pattern26. The AC modulation present in the returned secondary electron emission beam is in the form of an amplitude and phase modulated wave whose frequency is substantially that of the impinging acoustic energy and the signals may be rectified, amplified and displayed using conventional television techniques.

Referring next to FIG. 3 the illustrative embodiment and operation of the invention for acoustic viewing systems will now be described. As previouslynoted object 6 under surveillance illuminated by appropriate sound source means provides reflected focused acoustic energy rays 28 impinging on the exposed interface of transducer plate 12. The transducer plate for maximum power transference desirably has a resonance at a selected acoustic frequency (0,. This facilitates storage of vibrational energy within the plate material. Conventionally, the plate is operated in the half-wavelength resonant mode for peak response.

Since the present invention discloses the use of a nonscanning electron beam, means for generation of a probing primary electron beam, such as a flood-type beam are provided. Such beam generation means 30 may comprise a suitable electron gun or photo-cathode. The emitted beam 32 is directed to crossed field deflection system 34 having oppositely disposed conductive plates biased by appropriate voltages to provide a transverse electric field indicated by a circle 36 orthogonal to the flow of the electron beam. The image converter device of the present invention is immersed in a uniform magnetic field disposed normal to this electric field and parallel to the beam trajectory as indicated by arrow 38. The combined electric and magnetic fields provide an integrated adiabatic motion and deflect the flood beam sideways to uniformly and continuously sample the acoustic induced image voltage potentials across the transducer plate 12. To avert in-line reflection of the probing electron beam back to its source the acoustic transducer plate is offset in relation to the beam generation means. The deflected probing flood beam indicated by rays 40 will impinge on the transducer plate and yield an acoustically modulated secondary electron beam 42 representing a converted electrical signal pattern. Appropriate selection of the transducer plate material properties, as well as biasing potentials, will create the predetermined voltage condition for optimizing secondary electron emission. Deposition of a sensitized surface on the probed side of the transducer plate may also be practiced. The idealized condition will be one wherein the bombardment potential of the plate is adjusted to assume a steady DC bias at a stable secondary emission crossover state around a ratio value of unity. This crossover state can either be that of the material itself or an artificial intermediate crossover state created by the presence of a suitably biased mesh screen member adjacent to the transducer plate.

The returned acoustically induced voltage modulated secondary electron emission beam indicated by rays 44 is deflected by the crossed field system to impinge on correlator section 46 having image orthicon type components. An electric reference drive signal at the acoustic frequency w, is applied by means 48 to an element of this section such as a mesh screen member in front of the storage target plate electrode. There thus will emerge from this section integrated electrical output signals representative of the acoustic image. Such signals may be applied through appropriate processing circuits to display means 50 such as a cathode ray tube device.

Before proceeding with a more detailed analysis of the illustrative embodiment a brief review of secondary electron emission characteristics will be of assistance. In FIG. 4 curve 52 represents the relationship of the secondary electron emission ratio to the voltage potential of the striking primary electrons. This voltage potential represents the region between a cathode or any sensitized surface source of secondary electrons designated by the line 54 and a mesh screen member indicated by dashed line 56 disposed in front of the transducer plate in a vacuum 400 volts It will be noted that curve 52 has an intrinsic dip at point 58 below unity followed by what will be referred to as the first crossover point 60. The voltage potential at this crossover point is approximately primary volts. Another crossover point has been noted by the dashed line 62 at an energy voltage level of approximately 5,000 volts which offers a second possible operation mode. Such high voltages, however, present serious problems in practical embodiments and stability, as well as sensitivity.

An intermediate stable or artificial crossover point may be realized with a mesh screen member 56 at a biased voltage potential of approximately 400 volts relative to the adjacent transducer plate surface and will yield an effective secondary electron ratio crossover point indicated by A about the unity value. In the intermediate crossover region stable operation is assure with a high velocity beam of primary electrons.

In accordance with the present invention secondary electron emission characteristics are utilized to produce an acoustic modulated secondary electron beam impinging on the storage target plate member of an image orthicon correla tor section. With the intermediate crossover condition the transducer plate upon impingement by flood beam assumes on aDC basis a steady bias which is sufficient to achieve a surface potential above the mesh potential and reduce the effective secondary electron emission ratio to unity. An acoustic modulated surface potential, then, creates a modulation of this ratio about the unity value. Thus, without any acoustic image signal the effective secondary emission ratio is unity and the primary electron beam is essentially reflected back and deflected into the image orthicon correlator section. The storage target plate member of this section may also be biased at the artificial intermediate crossover condition by mesh screen members. A correlating drive signal corresponding to the acoustic frequency is injected into the correlator section and with the lack of acoustic image signals there will be no output electrical image signals from this section after integration of the reflected beam and the drive signals. Conversely, the presence of impinging acoustic image signals with a conversion to an electrical pattern by means of the modulation of the secondary electron ratio above and below unity results in a secondary electron beam proportional to the intensity of the induced acoustic signal voltages. Correlation of these signals and the electric drive signal at the acoustic frequency will result in an integrated electrical output image signal which is subsequently processed.

Referring to FIG. 5 further specific details of the construction, as well as operation, will be described. The probing flood beam emanates from a photocathode 64 at a voltage potential -V Since the entire device including the primary electron flood beam generation means is influenced by a uniform magnetic field B designated by arrow 66 the beam trajectory will be influenced similarly to traveling wave electron discharge devices having a linear magnetic field. In addition, suitable focusing and acceleration means such as cylindrical or plate members 68 are provided at a potential V,, for the primary electron beam. Similar focusing and accelerating means 70 at a substantially similar potential V, are centrally disposed between the primary electron beam generation means and the image orthicon correlator section 46. The return modulated beam is focused by means 72.

The uniform primary electron beam 32 is deflected in the crossed field system 34 before impinging on the piezoelectric plate 76. An illustrative embodiment for the crossed field deflection plates is shown in FIG. 6. Opposing conductive plates 78 and 80 have bowed surfaces 81 and 82 to provide a transverse electric field and thereby define an integrated adiabatic electricmagnetic field motion. Plate 78 is biased at a potential V V while opposing plate 80 is biased at V, V As a result of this relationship the combined fields will react on the beam 32. With the electric field represented by a vector x and the magnetic field by vector 2, then the beam will move sideways or in the y direction orthogonal to the first two vectors. Ideally, by well known adiabatic crossed field theory if the change in the E field experienced by the electron beam during one cyclotron is small enough, then the transverse motional energy remains substantially invariant and no deterioration of optics results because of amplified beam trajectories in the transverse plane.

After deflection, the primary electron beam is focused by means 84 to impinge upon the reverse side of the piezoelectric plate 76. A mesh screen member 86 is provided to bias the plate at, for example, the desired crossover point of the effective secondary electron emission ratio as hereinbefore discussed. The beam is desirably decelerated from a potential V,, to a target potential of V,. The bombardment potential is V V, and is adjusted to the value desired.

The returned secondary electron beam modulated by the acoustic image signals on the interface side of plate 76 are also deflected and impinge upon the storage target plate member 88 of the image orthicon correlator section 46. A mesh screen member 90 in front of the storage target plate member provides means for impressing of the electric drive signal V, (r) as a correlating signal. The resulting modulation of the beam, then, is proportional to the acoustic signal voltage.

The reverse side of the plate member 88 is also provided with a mesh screen member 92 to optimize the voltage modulation produced by the impinging secondary electron beam. The image orthicon correlator section further includes an electron beam gun 94 for generation of a scanning beam 96. The returned scanned integrated signals are processed through the electron multiplier section 98 to produce the correlation output signals. Deflecting and alignment magnetic coil means 100, illustrated partially only, in accordance with well known image orthicon tube techniques, together with a conductive member 102, completes this section of the overall embodiment. Further details as to an electrooptical correlator device of the image orthicon type envisaged in the present invention may be had by referring to U.S. Pat. No. 3,474,286, issued Oct. 21, 1969 to RC. I-Iergenrother and assigned to the assignee of the present invention. Although this device is utilized in the processing of optical signals the converted electron image pattern signals in the present acoustic image signal embodiment will be similarly processed at this scanning and multiplication stage of the overall system.

All the aforedescribed components are disposed within an envelope 104 with an internal evacuated atmosphere. In such applications of an acoustic viewing system involving large external pressures, the components may be readily adapted to such usage utilizing conventional pressurizing techniques.

There is thus disclosed a new and novel storage type acoustic image converter and viewing system of improved quality in definition and resolution heretofore unattainable. Many variations, modifications and alterations will be apparent to those skilled in the an relating to the disclosed device for use in the intended system. Such variations, therefore, are intended to be encompassed by the interpretation of the scope and breadth of the invention as set forth and defined in the appended claims.

What is claimed is:

1. In combination:

an envelope;

means for generation of a first beam of electrons disposed within said envelope;

means including a sensitized conversion member for generation of a reflected modulated beam of secondary electrons upon impingement by said first electron beam upon a surface of said member;

means for utilization of said reflected secondary electron beam disposed within said envelope;

and means providing a crossed electric and magnetic field region for deflection of said impinging and reflected beams disposed common to both said beam generation means and utilization means to provide principally nonreciprocal movement of each said beam relative to its emanating source.

2. The combination according to claim 1 wherein said crossed field deflection means comprise conductive plates having a substantially bowed configuration to provide a combined substantially adiabatic field.

3. The combination according to claim 1 wherein said utilization means include electrooptical means for storage, correlation and integration of electrical signals to derive an output signal representative of modulated electric field variations on said secondary electron beam.

4. The combination according to claim 1 wherein said first electron beam is of the nonscanning flood-type for uniformly and continuously providing a source of primary electrons.

5. The combination according to claim 1 wherein electrically conductive biasing means are disposed anterior to said sensitized conversion member in the path of said deflected first electron beam to produce a predetermined modulatory secondary electron emission characteristic.

6. The combination according to claim 1 wherein said first beam generation means and said utilization means are positioned along a similar side relative to said common crossed field deflection means and said secondary electron generation means are oppositely positioned in an offset manner relative thereto.

7. An acoustic image signal converter device comprising:

an evacuated envelope;

means for generating a beam of primary electrons disposed within said envelope;

transducer means for intercepting and converting impinging acoustic energy signals propagating in a medium outside said envelope into an acoustically induced electrical signal pattern;

crossed electric and magnetic field producing means for deflecting and directing said beam of primary electrons upon a surface of said transducer means as a flood-type beam to produce a reflected modulated secondary electron beam whose phase and amplitude is representative of said acoustically induced signal pattern;

and crossed electric and magnetic field producing means for deflecting and directing said acoustically modulated secondary electron beam into utilization means within said envelope;

said crossed field means being disposed common to both said beam generation means and utilization means; said utilization means including an electron signal integrator and correlator section having an electron target surface; means for impressing an electrical input reference signal to correlate signals on said modulated secondary electron beam;

means for electronically scanning the reverse side of said target surface;

and means for electronically multiplying and integrating said electrical signals to derive a correlated electrical output signal representative of the intercepted acoustic energy signals.

8. An acoustic image signal converter device according to claim 7 wherein said transducer means comprise a member of material having piezoelectric characteristics.

9. An acoustic image signal converter device according to claim 8 wherein said transducer means are biased by DC means to provide efiective secondary electron emission ratio modulating characteristics varying principally above and below a value of unity at an intermediate crossover region.

10. An acoustic image signal converter device according to claim 7 wherein said means for impressing an electrical input reference signal comprise a conductive mesh member disposed in front of the electron target surface of said integrator and correlator section.

1 1. An acoustic image viewing system comprising:

means for generation and direction of acoustic radiated energy probing a medium under examination;

means for focusing returning reflected acoustic energy rays;

means for sensing and converting said focused acoustic energy rays into electrical output signals representative of reflected acoustic energy signals;

means for utilizing said output signals;

said sensing and converting means comprising:

transducer means for producing an induced electrical signal pattern upon impingement by acoustic energy signals on a transducer surface exposed to the medium;

means for continuously and uniformly radiating the transducer means by a beam of primary electrons to produce a reflected acoustically induced modulated secondary electron beam directed to said utilization means;

said utilization means including means for electronically storing, scanning, integrating and correlating said modulated secondary electron beam electrical signals to derive an electrical output signal representative of an acoustic image;

means for visually displaying said electrical output signals;

and crossed electric and magnetic field producing means for deflecting and directing said primary and secondary electron beams in a nonreciprocal movement disposed common to both said primary electron beam generation and utilization means as well as said transducer means 12. An acoustic image viewing system according to claim 11 wherein said deflecting and directing means include spaced conductive plate members.

13. An acoustic image viewing system according to claim 11 wherein an electrical modulating correlating input reference signal at a predetermined acoustic frequency is impressed on said reflected secondary electron beam by a conductive biasing member disposed anterior to said utilization means.

14. An acoustic image viewing system according to claim 1 1 and means for electrically biasing said transducer means disposed in the path of said primary electron beam have an applied voltage potential sufficient to provide a substantially stable secondary electron emission ratio value on a DC basis at a crossover point around a value of unity other than the inherent crossover value of the transducer means without an applied bias.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,654,596 Dated April 4, 1972 Inventoflx) John M. osepchuk It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 5, line l8, after "vacuum" delete "400 volts" and insert environment and insert Z0 Signed and sealed this 29th day of August 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD M.FLETCHER,JR.

Commissioner of Patents Attesting Officer USCOMM'DC 5O376-P69 U.$. GOVERNMENT PRINYING OFFICE 1 I969 0-356-334 FORM 1 0-1050 (10-69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated April 4, 1972 Patent No. 3,654,596

Inven flx) John M. Osepchuk It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 18, after "vacuum" delete "400 volts" and insert environment Column 5, line 21, after "approximately" delete "primary" and insert 20 Signed and sealed this 29th day of August 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer 7 Commissioner of Patents )RM PC4050 (10-69) USCOMM-DC 60376-P6Q Q U.$. GOVERNMENT PRINTING OFFICE I969 0-355-334 

1. In combination: an envelope; means for generation of a first beam of electrons disposed within said envelope; means including a sensitized conversion member for generation of a reflected modulated beam of secondary electrons upon impingement by said first electron beam upon a surface of said member; means for utilization of said reflected secondary electron beam disposed within said envelope; and means providing a crossed electric and magnetic field region for deflection of said impinging and reflected beams disposed common to both said beam generation means and utilization means to provide principally nonreciprocal movement of each said beam relative to its emanating source.
 2. The combination according to claim 1 wherein said crossed field deflection means comprise conductive plates having a substantially bowed configuration to provide a combined substantially adiabatic field.
 3. The combination according to claim 1 wherein said utilization meAns include electrooptical means for storage, correlation and integration of electrical signals to derive an output signal representative of modulated electric field variations on said secondary electron beam.
 4. The combination according to claim 1 wherein said first electron beam is of the nonscanning flood-type for uniformly and continuously providing a source of primary electrons.
 5. The combination according to claim 1 wherein electrically conductive biasing means are disposed anterior to said sensitized conversion member in the path of said deflected first electron beam to produce a predetermined modulatory secondary electron emission characteristic.
 6. The combination according to claim 1 wherein said first beam generation means and said utilization means are positioned along a similar side relative to said common crossed field deflection means and said secondary electron generation means are oppositely positioned in an offset manner relative thereto.
 7. An acoustic image signal converter device comprising: an evacuated envelope; means for generating a beam of primary electrons disposed within said envelope; transducer means for intercepting and converting impinging acoustic energy signals propagating in a medium outside said envelope into an acoustically induced electrical signal pattern; crossed electric and magnetic field producing means for deflecting and directing said beam of primary electrons upon a surface of said transducer means as a flood-type beam to produce a reflected modulated secondary electron beam whose phase and amplitude is representative of said acoustically induced signal pattern; and crossed electric and magnetic field producing means for deflecting and directing said acoustically modulated secondary electron beam into utilization means within said envelope; said crossed field means being disposed common to both said beam generation means and utilization means; said utilization means including an electron signal integrator and correlator section having an electron target surface; means for impressing an electrical input reference signal to correlate signals on said modulated secondary electron beam; means for electronically scanning the reverse side of said target surface; and means for electronically multiplying and integrating said electrical signals to derive a correlated electrical output signal representative of the intercepted acoustic energy signals.
 8. An acoustic image signal converter device according to claim 7 wherein said transducer means comprise a member of material having piezoelectric characteristics.
 9. An acoustic image signal converter device according to claim 8 wherein said transducer means are biased by DC means to provide effective secondary electron emission ratio modulating characteristics varying principally above and below a value of unity at an intermediate crossover region.
 10. An acoustic image signal converter device according to claim 7 wherein said means for impressing an electrical input reference signal comprise a conductive mesh member disposed in front of the electron target surface of said integrator and correlator section.
 11. An acoustic image viewing system comprising: means for generation and direction of acoustic radiated energy probing a medium under examination; means for focusing returning reflected acoustic energy rays; means for sensing and converting said focused acoustic energy rays into electrical output signals representative of reflected acoustic energy signals; means for utilizing said output signals; said sensing and converting means comprising: transducer means for producing an induced electrical signal pattern upon impingement by acoustic energy signals on a transducer surface exposed to the medium; means for continuously and uniformly radiating the transducer means by a beam of primary electrons to produce a reflected acoustically induced modulated secondary electron beam directEd to said utilization means; said utilization means including means for electronically storing, scanning, integrating and correlating said modulated secondary electron beam electrical signals to derive an electrical output signal representative of an acoustic image; means for visually displaying said electrical output signals; and crossed electric and magnetic field producing means for deflecting and directing said primary and secondary electron beams in a nonreciprocal movement disposed common to both said primary electron beam generation and utilization means as well as said transducer means.
 12. An acoustic image viewing system according to claim 11 wherein said deflecting and directing means include spaced conductive plate members.
 13. An acoustic image viewing system according to claim 11 wherein an electrical modulating correlating input reference signal at a predetermined acoustic frequency is impressed on said reflected secondary electron beam by a conductive biasing member disposed anterior to said utilization means.
 14. An acoustic image viewing system according to claim 11 and means for electrically biasing said transducer means disposed in the path of said primary electron beam have an applied voltage potential sufficient to provide a substantially stable secondary electron emission ratio value on a DC basis at a crossover point around a value of unity other than the inherent crossover value of the transducer means without an applied bias. 